Improved response of plaque psoriasis after multiple treatments with topical 5-aminolaevulinic acid photodynamic therapy

We investigated the clinical response of 10 patients with plaque psoriasis to multiple treatments with photodynamic therapy, using topical application of 5-aminolaevulinic acid followed by exposure to broad-band visible radia tion. Treatment was performed up to 3 times per week, with a maximum of 12 treatments, using a light dose of 8 Jcm(-2) delivered at a dose-rate of 15 mWcm(-2). Eight patients showed a clinical response. Out of 19 treated site s, 4 cleared, 10 responded but did not clear and 5 showed no improvement. O f the 4 sites that cleared only 1 did so fully, after 7 treatments, 45 days after the start of therapy. Of the 10 sites that responded partially, the greatest reduction in scale, erythema and induration index occurred after a minimum of 3 and a maximum of 8 treatments. The intensity of 5-aminolaevul inic acid-induced protoporphyrin IX fluorescence, recorded prior to the fir st treatment, varied between sites on the same patient as well as between p atients. There was also a variation in fluorescence intensity recorded from the same site immediately prior to subsequent treatments, although the pre treatment levels generally decreased as the study progressed and then incre ased as psoriasis relapsed. Biopsies confirmed that fluorescence was locali zed throughout the epidermis and stratum corneum, but the level was not con sistent between sections taken within the same biopsy. We also observed flu orescence at sites distant from the ones that received 5-aminolaevulinic ac id, which was not present prior to the start of the treatment programme, bu t found no evidence of elevated levels of plasma porphyrins. The level of d iscomfort associated with this therapy increased with increasing values of the calculated photodynamic dose, defined as the product of the initial pho tosensitizer concentration and the percentage reduction in fluorescence fol lowing irradiation. Therefore, although clinical efficacy improved with mul tiple treatments, unpredictable response and patient discomfort make ALA-PD T unsuitable for the treatment of psoriasis.